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8.2: Human Inheritance

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Lesson 8.2: True or False

Name___________________ Class______________ Date________

Write true if the statement is true or false if the statement is false.

_____ 1. Characteristics that are encoded in DNA are called genetic diseases.

_____ 2. Widow's peak and hitchhiker's thumb are multiple allele traits.

_____ 3. Single-gene X-linked traits have a different pattern of inheritance than single-gene autosomal traits.

_____ 4. Most human traits have more complex modes of inheritance than simple Mendelian inheritance.

_____ 5. Because it is a polygenic trait, human height can be represented by a bell-shaped graph.

_____ 6. Pleiotropy is when a more than one gene affects a single trait.

_____ 7. Most genetic disorders are controlled by dominant alleles.

_____ 8. Triple X syndrome results in XYXX males.

_____ 9. A karyotype is a picture of a cell's chromosomes.

_____ 10. A recessive X-linked allele is always expressed in males.

_____ 11. The alleles for ABO blood type are the A, B, AB and O alleles.

_____ 12. Amniocentesis can be used to see if the mother has any genetic abnormalities.

_____ 13. Down syndrome is also known as trisomy 21.

_____ 14. A mutant recessive allele is not expressed in people who inherit just one copy of it.

_____ 15. Epistasis is when one gene affects the expression of another gene.

Lesson 8.2: Critical Reading

Name___________________ Class______________ Date________

Read these passages from the text and answer the questions that follow.

Genetic Disorders

Many genetic disorders are caused by mutations in one or a few genes. Other genetic disorders are caused by abnormal numbers of chromosomes.

Genetic Disorders Caused by Mutations

Table below lists several genetic disorders caused by mutations. Some of the disorders are caused by mutations in autosomal genes, others by mutations in X-linked genes. Which disorder would you expect to be more common in males than females?

Genetic Disorder Direct Effect of Mutation Signs and Symptoms of the Disorder Mode of Inheritance
Marfan syndrome defective protein in connective tissue heart and bone defects and unusually long, slender limbs and fingers autosomal dominant
Sickle cell anemia abnormal hemoglobin protein in red blood cells sickle-shaped red blood cells that clog tiny blood vessels, causing pain and damaging organs and joints autosomal recessive
Vitamin D-resistant rickets lack of a substance needed for bones to absorb minerals soft bones that easily become deformed, leading to bowed legs and other skeletal deformities X-linked dominant
Hemophilia A reduced activity of a protein needed for blood clotting internal and external bleeding that occurs easily and is difficult to control X-linked recessive

Few genetic disorders are controlled by dominant alleles. A mutant dominant allele is expressed in every individual who inherits even one copy of it. If it causes a serious disorder, affected people may die young and fail to reproduce. Therefore, the mutant dominant allele is likely to die out of the population. A mutant recessive allele, such as the allele that causes sickle cell anemia, is not expressed in people who inherit just one copy of it. These people are called carriers. They do not have the disorder themselves, but they carry the mutant allele and can pass it to their offspring. Thus, the allele is likely to pass on to the next generation rather than die out.

Chromosomal Disorders

Mistakes may occur during meiosis that result in nondisjunction. This is the failure of replicated chromosomes to separate during meiosis II. Some of the resulting gametes will be missing a chromosome, while others will have an extra copy of the chromosome. If such gametes are fertilized and form zygotes, they usually do not survive. If they do survive, the individuals are likely to have serious genetic disorders. Table below lists several genetic disorders that are caused by abnormal numbers of chromosomes.

Genetic Disorder Genotype Phenotypic Effects
Down syndrome extra copy (complete or partial) of chromosome 21 developmental delays, distinctive facial appearance, and other abnormalities
Turner’s syndrome one X chromosome but no other sex chromosome (XO) female with short height and infertility (inability to reproduce)
Triple X syndrome three X chromosomes (XXX) female with mild developmental delays and menstrual irregularities
Klinefelter’s syndrome one Y chromosome and two or more X chromosomes (XXY, XXXY) male with problems in sexual development and reduced levels of the male hormone testosterone

Having the wrong number of chromosomes causes the genetic disorders described in Table above. Most chromosomal disorders involve the X chromosome. Look back at the X and Y chromosomes and you will see why. The X and Y chromosomes are very different in size, so nondisjunction of the sex chromosomes occurs relatively often.

Questions

1. What two main ways cause genetic disorders?

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2. What are the signs and symptoms of sickle cell anemia?

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3. Why are few genetic disorders controlled by dominant alleles?

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4. Explain what causes chromosomal disorders.

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5. Describe the cause and symptoms of Down syndrome.

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Lesson 8.2: Multiple Choice

Name___________________ Class______________ Date________

Circle the letter of the correct choice.

  1. Which of the following statements concerning genetic disorders is correct? (1) Many genetic disorders are caused by mutations in one or a few genes. (2) Some genetic disorders are caused by abnormal numbers of chromosomes. (3) Most genetic disorders are caused by dominant alleles. (4) Chromosomal disorders result from nondisjunction during mitosis.
    1. 1 only
    2. 1 and 2
    3. 1, 2, and 3
    4. all four statements are correct
  2. Single-gene X-linked traits have a different pattern of inheritance than single-gene autosomal traits because
    1. females have just one X chromosome.
    2. females have two X chromosomes.
    3. males have two X chromosomes.
    4. males have just one X chromosome.
  3. ABO blood type is a multiple allele trait. Which of the following are possible ABO blood type phenotypes? (1) A, (2) B, (3) AB, (4) O, (5) AO, (6) BO
    1. 1 and 2 only
    2. 3 and 4 only
    3. 5 and 6 only
    4. 1, 2, 3, and 4
  4. Hemophilia A is due to
    1. a defective protein in connective tissue.
    2. abnormal hemoglobin protein in red blood cells.
    3. reduced activity of a protein needed for blood clotting.
    4. lack of a substance needed for bones to absorb minerals.
  5. Down syndrome is due to
    1. nondisjunction of chromosome 21.
    2. nondisjunction of the X chromosome.
    3. one Y chromosome and two or more X chromosomes.
    4. nondisjunction of the Y chromosome.
  6. Which of the following statements is true?
    1. A recessive X-linked allele is always expressed in males.
    2. Males will have two alleles for any X-linked trait.
    3. Males must inherit two copies of a recessive X-linked allele to express the recessive trait.
    4. X-linked recessive traits are less common in males than females.
  7. In a polygenic trait, such as adult height, most people
    1. will have a phenotype close to the average.
    2. will have the dominant phenotype.
    3. will have a heterozygous genotype.
    4. will be 5 feet 8 inches tall.
  8. A mother has red-green color blindness. Her husband is not affected.
    1. Half of their daughters will have red-green color blindness.
    2. All of their daughters will have red-green color blindness.
    3. All of their sons will have red-green color blindness.
    4. All of their children will have red-green color blindness.

Lesson 8.2: Vocabulary I

Name___________________ Class______________ Date________

Match the vocabulary word with the proper definition.

Definitions

_____ 1. involves inserting normal genes into cells with mutant genes

_____ 2. when one gene affects the expression of another gene

_____ 3. the inheritance of traits controlled by a single gene with two alleles

_____ 4. trait controlled by genes on the sex chromosomes

_____ 5. when a single gene affects more than one trait

_____ 6. an example of a multiple allele trait

_____ 7. the failure of replicated chromosomes to separate during meiosis

_____ 8. trait controlled by a gene on one of the 22 human autosomes

_____ 9. characteristics (traits) encoded in DNA

_____ 10. shows how a trait is passed from generation to generation within a family

_____ 11. red-green color blindness

_____ 12. traits controlled by a single gene with more than two alleles

Terms

a. ABO blood type

b. autosomal trait

c. epistasis

d. gene therapy

e. genetic trait

f. Mendelian inheritance

g. multiple allele trait

h. nondisjunction

i. pedigree

j. pleiotropy

k. sex-linked trait

l. X-linked trait

Lesson 8.2: Vocabulary II

Name___________________ Class______________ Date________

Fill in the blank with the appropriate term.

1. Characteristics that are encoded in DNA are called genetic ____________.

2. Sex-linked traits are usually associated with genes on the ____________ chromosome.

3. Traits controlled by a single gene with more than two alleles are called multiple ____________ traits.

4. Mendelian inheritance refers to the inheritance of traits controlled by a single ____________ with two ____________.

5. ABO blood type is a ____________ allele trait.

6. Sickle cell anemia results in an abnormal ____________ protein in red blood cells.

7. Hemophilia A results in reduced activity of a protein needed for blood ____________.

8. ____________ is caused by an extra copy of chromosome 21.

9. An example of a recessive ____________ trait would be red-green color blindness.

10. Human height is an example of a ____________ trait.

11. Many genetic disorders are caused by ____________ in one or a few genes.

12. Nondisjunction occurs during ____________.

Lesson 8.2: Critical Writing

Name___________________ Class______________ Date________

Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences.

Explain two complex modes of human inheritance. Give examples.

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